The ease and economics of fabricating gears, cams, bearings, slides, ratchets, and the like with injection moldable thermoplastic resins has led to widespread displacement of metals for these applications. In addition to the inherent processing advantages, parts made from these thermoplastic materials have the ability to dampen shock and vibration, reduce part weight, run with less power, provide corrosion resistance, and run quietly. Polycarbonate resins, because of their many excellent physical and mechanical properties such as, for example, toughness, flexibility, impact strength, and high heat resistance, are particularly well suited for this purpose. However, polycarbonate resin parts, akin to other thermoplastic resin parts, are subject to greater wear than comparable metal parts when brought into repeated contact with other moving parts such as those fabricated from metal or thermoplastics.
It would thus be very advantageous if a polycarbonate composition could be provided which, when fabricated into a mechanical moving part, exhibits many of the advantageous properties of conventional neat polycarbonates and also exhibits improved wear resistance.
Attempts have been made to improve the wear resistance of polycarbonate resins by blending them with various other resins. These attempts have generally not been unqualified successes. This is due to the fact that in order to provide useful polycarbonate blends exhibiting improved wear resistance the material admixed with the polycarbonate resin must not only improve the wear resistance of polycarbonate resin but must also be compatible with polycarbonates, i.e., must not significantly adversely affect most of the advantageous properties of polycarbonate, and must be combinable with polycarbonate resin in amounts which are effective to improve the wear resistance of said resin.
Thus, for example, while some materials are both compatible with polycarbonate resins and are combinable therewith over a wide range of concentrations they do not positively upgrade the wear resistance of these resins. Indeed, some of these materials adversely affect the wear resistance of polycarbonates. Other materials, while improving the wear resistance of polycarbonates, are not compatible with polycarbonates or are not combinable therewith in amounts which are effective to improve the wear resistance thereof. Still other materials, while being compatible with polcarbonates and combinable therewith over wide concentrations, need be present in such large amounts in order to positively upgrade the wear resistance that they materially affect and change the basic nature and properties of the polycarbonate.
Thus, in order to provide a useful polycarbonate composition exhibiting improved wear resistance not only is the nature of the material itself critical but its concentration in the blends is also of vital importance.
Furthermore, the degree of effectiveness as a wear improving agent varies greatly among the materials which are compatible with polycarbonate resins, are combinable with polycarbonate resins in amounts which are effective to positively upgrade the wear resistance of polycarbonate resins, and which positively improve the wear resistance of these resins. That is to say some materials are much more effective in positively upgrading the wear resistance of polycarbonate resins than others when admixed with the polycarbonate resin in substantially identical amounts.
There does not appear to be any great degree of predicatbility or certainty as to how a particular material will function, as regards its ability to improve the wear resistance of polycarbonate resins, when said material is admixed with polycarbonates. The empirical approach is generally the rule rather than the exception in this field
It is, therefore, an object of the instant invention to provide useful polycarbonate resin compositions which exhibit improved wear resistance when fabricated into gears, cams, bearings, and the like.
U.S. Pat. No. 4,220,583 to Mark discloses translucent and thermally stable polycarbonate compositions comprising an admixture of an aromatic polycarbonate and a minor amount, i.e., from about 0.01 to about 5 weight percent based on the weight of the polycarbonate composition, of a partially fluorinated polyolefin. Mark did not recognize that blends of polycarbonate resin and amounts of partially fluorinated polyolefin in excess of 5 weight percent have improved resistance to wear.